1. Field of the Invention
This invention relates to a semiconductor device such as a light-emitting diode (LED) and also relates to a method of manufacturing such semiconductor element.
2. Description of the Related Art
Light-emitting devices equipped with LED elements are used in, for example, illumination, backlighting and industrial equipment. Efforts are expended to increase the brightness of light-emitting elements in such light-emitting devices. LED elements are manufactured by using, for example, a metal-organic chemical vapor deposition (MOCVD) method to deposit a semiconductor layer of AlGaInP or GaN by epitaxial growth on a GaAs substrate, sapphire substrate or other growth substrate. In an LED element manufactured in this way, light emitted from the light emission layer is absorbed in the growth substrate so that the efficiency of light extraction is reduced. In addition, the efficiency of hear dissipation is poor because of the low thermal conductivity of the growth substrate.
In order to resolve the above-mentioned problems, LED elements are manufactured in the following manner: a semiconductor layer grown on a growth substrate is laminated on a supporting substrate that has high thermal conductivity with a light-reflecting material intervening, and then the growth substrate is removed. Such LED elements are disclosed in, for example, Japanese Patent Application Publication (Kokai) No. 2006-237419.
When semiconductor elements are manufactured using supporting substrates as described above, a eutectic crystal such as AuSn is used to bond the semiconductor layer to a supporting substrate with thermal conductivity. This bonding is referred to as “eutectic bonding” in this specification. In eutectic bonding, the eutectic crystal material is melted or softened at a high temperature at or above the melting point of the AuSn used in bonding, in order to perform satisfactory bonding with few voids in the bond portion.
FIG. 1 of the accompanying drawings shows a scanning electron microscopy (SEM) image (20,000×) of a cross section of a bonding portion after general eutectic bonding is performed. In this SEM image, a layer containing large amounts of Au appears pale and whitish, whereas layers containing large amounts of Sn appear darker and blackish. As shown in FIG. 1, when performing eutectic bonding using AuSn, a layer containing a large amount of Sn (that is, an Sn-rich layer), a layer containing a large amount of Au (that is, an Au-rich layer), and another Sn-rich layer are formed in the bonding portion, in order from the semiconductor layer side, to form a sandwich structure in which an Au-rich layer is sandwiched by two Sn-rich layers. Sn has a low(er) thermal conductivity (64 W/m·K) compared with that of Au (295 W/m·K), and so the layer adjacent to the semiconductor layer has low thermal conductivity. As a result, dispersion of heat from the semiconductor layer is impeded, and the efficiency of heat dissipation is poor.